Polishing apparatus and method of polishing work piece

ABSTRACT

The polishing apparatus is capable of changing a pH value of slurry to adjust polishing rate and polishing a work piece with high flatness. The polishing apparatus comprises: a pressure vessel; a polishing plate provided in the pressure vessel; a pressing plate pressing a work piece onto the polishing plate; a driving unit relatively moving the polishing plate with respect to the pressing plate so as to polish the work piece; a gas supplying source supplying an alkaline gas or an acid gas into the pressure vessel; a gas discharging section discharging the supplied gas from the pressure vessel; and a slurry supplying unit supplying slurry onto the polishing plate. A pH value of the slurry is adjusted by dissolving the alkaline gas or the acid gas in the slurry.

BACKGROUND OF THE INVENTION

The present invention relates to a polishing apparatus and a method ofpolishing a work piece, e.g., silicon wafer.

In conventional polishing apparatuses for polishing work pieces, e.g.,silicon wafers, atmospheric conditions of the apparatuses or theirpolishing sections, e.g., pressure, temperature, humidity, are notspecially controlled. Therefore, especially in chemical-mechanicalpolishing apparatuses, stable machining characteristics cannot begained. To solve the problem, the inventors of the present inventionhave invented a pressure vessel type polishing apparatus, which has apressure vessel whose atmosphere can be controlled (see Japanese PatentGazette No. 2003-225859). The polishing apparatus is capable ofimproving polishing efficiency.

In case of chemical-mechanical polishing, a pH value of slurry greatlyinfluences polishing rate and quality of products. In a conventionalopen-type polishing apparatus, a pH value of slurry delicately changesaccording to the atmospheric conditions. Therefore, it is difficult toprecisely control the pH value of the slurry.

Further, in the case of chemical-mechanical polishing, it usually takes2-7 minutes to gain normal machining characteristics after dressing apolishing pad. After dressing the polishing pad, a surface of thepolishing pad is cleaned by pure water, so it takes a long time tocompletely remove used slurry therefrom. Especially, in case of changingto different type slurry during the chemical-mechanical polishingprocess, it takes 10 minutes or more to completely exchange slurry.

Especially, in the pressure vessel type polishing apparatus, polishingconditions must be rapidly changed without exchanging slurry.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a pressure vessel typepolishing apparatus, which is capable of changing a pH value of slurryto adjust polishing rate and polishing a work piece with high flatness,and a method of polishing a work piece with the polishing apparatus.

Another object is to provide a pressure vessel type polishing apparatus,which is capable of suitably coping with different polishing conditionswithout exchanging slurry, and a method of polishing a work piece withthe polishing apparatus.

To achieve the object, the present invention has following structures.

Namely, a first basic structure of the polishing apparatus of thepresent invention comprises:

a pressure vessel having a lid which opens or closes the pressurevessel;

a polishing plate being provided in the pressure vessel;

a pressing plate being provided on the polishing plate, the pressingplate pressing a work piece, which has been set between the polishingplate and the pressing plate, onto the polishing plate;

a driving unit relatively moving the polishing plate with respect to thepressing plate so as to polish the work piece;

a gas supplying source being connected to the pressure vessel, the gassupplying source supplying an alkaline gas or an acid gas into thepressure vessel;

a gas discharging section discharging the supplied gas from the pressurevessel; and

a slurry supplying unit supplying slurry onto the polishing plate,

wherein a pH value of the slurry is adjusted by dissolving the alkalinegas or the acid gas in the slurry.

A second basic structure of the polishing apparatus comprises:

a pressure vessel having a lid which opens or closes the pressurevessel;

a polishing plate being provided in the pressure vessel;

a pressing plate being provided on the polishing plate, the pressingplate pressing a work piece, which has been set between the polishingplate and the pressing plate, onto the polishing plate;

a driving unit relatively moving the polishing plate with respect to thepressing plate so as to polish the work piece;

a gas supplying source being connected to the pressure vessel, the gassupplying source supplying an alkaline gas or an acid gas into thepressure vessel;

a gas discharging section discharging the supplied gas from the pressurevessel; and

a pure water supplying unit supplying pure water onto the polishingplate,

wherein a pH value of the pure water is adjusted by dissolving thealkaline gas or the acid gas in the pure water so as to use the purewater as slurry.

A first method of polishing a work piece, in a polishing apparatuscomprising: a pressure vessel having a lid which opens or closes thepressure vessel; a polishing plate being provided in the pressurevessel; a pressing plate being provided on the polishing plate, thepressing plate pressing a work piece, which has been set between thepolishing plate and the pressing plate, onto the polishing plate; adriving unit relatively moving the polishing plate with respect to thepressing plate so as to polish the work piece; a gas supplying sourcebeing connected to the pressure vessel, the gas supplying sourcesupplying an alkaline gas or an acid gas into the pressure vessel; a gasdischarging section discharging the supplied gas from the pressurevessel; and a slurry supplying unit supplying slurry onto the polishingplate, comprises the step of:

supplying the alkaline gas or the acid gas into the pressure vessel fromthe gas supplying source so as to adjust the pH value of the slurry.

A second method of polishing a work piece, in a polishing apparatuscomprising: a pressure vessel having a lid which opens or closes thepressure vessel; a polishing plate being provided in the pressurevessel; a pressing plate being provided on the polishing plate, thepressing plate pressing a work piece, which has been set between thepolishing plate and the pressing plate, onto the polishing plate; adriving unit relatively moving the polishing plate with respect to thepressing plate so as to polish the work piece; a gas supplying sourcebeing connected to the pressure vessel, the gas supplying sourcesupplying an alkaline gas or an acid gas into the pressure vessel; a gasdischarging section discharging the supplied gas from the pressurevessel; and a pure water supplying unit supplying pure water onto thepolishing plate, comprises the step of:

supplying the alkaline gas or the acid gas into the pressure vessel fromthe gas supplying source so as to adjust the pH value of the pure waterand use the pure water as slurry.

In the polishing apparatus and the method of the present invention, thepolishing apparatus is capable of suitably and rapidly coping withvarious polishing conditions without exchanging slurry in the pressurevessel. Therefore, various types of polishing can be efficientlyperformed in the polishing apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexamples and with reference to the accompanying drawings, in which:

FIG. 1 is a front view of a polishing apparatus of an embodiment of thepresent invention;

FIG. 2 is a plan view of the polishing apparatus, in which a lid isopened;

FIG. 3 is a plan view of a bell jar;

FIG. 4 is an explanation view a pressure source connected to the belljar;

FIG. 5 is an explanation view of a driving unit of another example;

FIG. 6 is an explanation view of the driving unit of other example;

FIG. 7 is an explanation view of a mechanism for moving a polishingplate;

FIG. 8 is a sectional view of a press-type pressing plate;

FIG. 9 is a graph showing a relationship between air pressure andpolishing rate;

FIG. 10 is a graph showing a relationship between oxygen gas pressureand polishing rate;

FIG. 11 is a graph showing a relationship between inner pressure of thebell jar, pH values of slurry and polishing rate;

FIG. 12 is a graph showing a relationship between pH values of theslurry and polishing rate;

FIG. 13 is a graph showing a relationship between pH values of theslurry and polishing rate;

FIGS. 14-17 are sectional views, which show a process of implantingcopper cables in a substrate, wherein FIG. 14 shows a state in which anoutermost copper layer is not polished, FIG. 15 shows a state in whichthe outermost copper layer is polished toward a barrier metal layer,FIG. 16 shows a state in which top parts of the barrier metal layer areexposed, and FIG. 17 shows a state in which the top parts of the barriermetal layer are removed;

FIGS. 18-21 are sectional views, which show a process of polishing aSiO₂ film formed on copper cables, wherein FIG. 18 shows a state inwhich the SiO₂ film is not polished, FIG. 19 shows a state in which theSiO₂ film is polished toward stop layers, FIG. 20 shows a state in whichthe stop layers are exposed, and FIG. 21 shows a state in which the stoplayers are removed; and

FIG. 22 is an explanation view of another embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

FIG. 1 is a front sectional view of a polishing apparatus 10 of anembodiment of the present invention; FIG. 2 is a plan view of thepolishing apparatus, in which a lid is opened; and FIG. 3 is a plan viewof a bell jar.

The bell jar 12 has a lid 14 and acts as a pressure vessel capable ofbearing increase and reduce of pressure therein. The lid 14 is pivotablyattached to a body proper 16 of the bell jar 12 by a shaft 15 so as toopen and close the body proper 16.

A lower end of a clamping bolt 18 is pivotably attached to the bodyproper 16 by a shaft 21; an upper end of the bolt 18 is capable ofentering a gap between U-shaped forks of a fixed arm 19. By turning anut 20, the lid 14 can air-tightly close the body proper 16. In thepresent embodiment, six clamping bolts 18 are provided with angularseparations of 60 degrees.

The body proper 16 is made of steel having a prescribed thickness andformed into a bottomed cylindrical shape. A top plate of the lid 14 iscurved upward. With this pressure-resisting structure, the bell jar 12can act as the pressure vessel. A bottom section 16 a of the body proper16 is a flat plate, and its thickness is much thicker than that of acylindrical section so as to bear inner pressure.

Note that, the shape of the bell jar 12 is not limited to thecylindrical shape. Other pressure vessels which have enoughpressure-resisting structure can be employed in the present invention.

A polishing plate 23 is provided in the bell jar 12.

A polishing cloth or a polishing pad (not shown), which is made of aknown material, is adhered on an upper face of the polishing plate 23.

A connecting member 24, which is formed into a cylindrical shape, isfixed on a bottom face of the polishing plate 23. The connecting member24 is connected to a rotary shaft 26, which is rotatably held by abearing 25 of the bottom section 16 a, by a key 27. With this structure,the polishing plate 23 is rotated together with the rotary shaft 26. Asymbol 28 stands for a sealing member.

A lower end part of the polishing plate 23 is supported by a thrustbearing 29. A supporting member 30 is provided on the bottom section 16a, and the thrust bearing 29 is provided on the supporting member 30.

A cover 31 encloses an outer circumferential face of the polishing plate23 so as to remain prescribed amount of slurry on the polishing plate23. Note that, the cover 31 may be omitted.

A supporting base 32 supports the bell jar 12 and has four legs 32 a. Anadjustable bolt 33 is provided to a lower end of each leg 32 a so as toadjust height of the supporting base 32 and levelness of the bell jar12.

A motor 35, which acts as a driving unit, is attached to the supportingbase 32. A motor shaft of the motor 35 is connected to the rotary shaft26, so that the motor 35 can rotate the polishing plate 23. In thepresent embodiment, the motor 35 is provided outside of the bell jar 12,but the motor 35 may be provided in the bell jar 12.

A pressing plate 36 for pressing a work piece (not shown) is provided onthe polishing plate 23. The pressing plate 36 applies own weight to thepolishing plate 23 as a pressing force. The work piece to be polished isset or sandwiched between the polishing plate 23 and the pressing plate36.

A plurality of weights 37 are mounted on the pressing plate 36 so as toadjust the pressing force. Note that, number of the weights 37 isoptionally determined on the basis of polishing conditions.

A roller 38, which is coaxial with the polishing plate 23, and a roller39, which is provided above an outer edge of the polishing plate 23,contact an outer edge of the pressing plate 36, so that the pressingplate 36 can be held at a prescribed position on the polishing plate 23.The rollers 38 and 39 are rotatably held by an arc-shaped arm 40provided in the bell jar 12.

In FIG. 2, the polishing plate 23 is rotated in a direction “A”. Byrotating the polishing plate 23, the pressing plate 36 too is rotated,about its own axis, in the same direction.

Note that, the roller 38 may be rotated by a motor (not shown) so as tocompulsorily rotate the pressing plate 36, which contacts the roller 38,in a prescribed direction.

A proper amount of slurry is stored in the body proper 16. In thepresent embodiment, a lower part of the body proper 16 acts as a slurrystoring section 16 b (see FIG. 4).

As shown in FIG. 4, the slurry stored in the body proper 16 iscirculated by a circulation pump 43.

The circulation pump 43 is connected to a pipe 44, which is connected tothe slurry storing section 16 b, and a pipe 45, which is connected to anupper part of the body proper 16. The slurry stored in the slurrystoring section 16 b is drawn by the pump 43 and supplied onto thepolishing plate 23 via the pipe 45. The slurry, which has been used topolish the work piece, is collected in the slurry storing section 16 b.

The slurry storing section 16 b, the circulation pump 43 and the pipes44 and 45, etc. constitute a slurry supplying unit. Note that, a symbol44 a shown in FIG. 1 stands for a connecting section of the pipe 44.

The slurry storing section 16 b, of course, may be provided outside ofthe bell jar 12.

In FIG. 4, a symbol 47 stands for a pressurizing unit acts as a pressuresource; a symbol 48 stands for a gas discharging section.

The pressurizing unit 47 is connected to the body proper 16 via a pipe49 so as to introduce a pressurizing gas (fluid) into the bell jar 12.In the present embodiment, air, oxygen, nitrogen, argon, etc. areemployed as the pressurizing gasses. Other gasses may be optionallyemployed. The pressurizing gasses are selected and supplied into thebell jar 12 by a switching valves (not shown). A pressure reductionvalve 51 is provided so as to supply the fluid into the bell jar 12 withpredetermined pressure. Symbols 52 and 53 are valves, and a symbol 54 isa flow control valve capable of controlling amount of flow of the fluid.

Note that, a mixed gas may be employed as the fluid.

The gas discharging section 48 is connected to a part of the pipe 49,which is located between the valves 52 and 53. A symbol 56 stands for avalve.

The gas discharging section 48 includes a vacuum pump.

Note that, a symbol 49 a shown in FIG. 1 stands for a connecting sectionof the pipe 49.

By closing the valve 56 and opening the valves 52 and 53, thepressurized fluid can be introduced into the bell jar 12, so that innerpressure of the bell jar 12 can be increased. On the other hand, byclosing the valve 52 and opening the valves 53 and 56, the gasdischarging unit 48 sucks the fluid in the bell jar 12, so that theinner pressure of the bell jar 12 can be reduced.

A pressure gauge 57, which acts as a measuring equipment, measures theinner pressure of the bell jar 12. Other equipments for measuringtemperature, humidity, etc. may be provided if required.

A safety valve 58 releases the pressurized fluid outside when the innerpressure of the bell jar 12 exceeds a prescribed value. A symbol 60 astands for a viewing window (see FIG. 3).

In FIG. 4, a symbol 71 stands for an ammonia gas bombe, which acts as analkaline gas supplying source; a symbol 72 stands for a carbonic acidgas bombe, which acts as an acid gas supplying source.

The gas supplying source 71 is connected to the bell jar 12 via pipes 73and 74. A valve 75 is provided to the pipe 73; a valve 76 is provided tothe pipe 74.

The gas supplying source 72 is connected to the bell jar 12 via pipes 74and 77. A valve 78 is provided to the pipe 77.

By closing the valve 78 and opening the valves 75 and 76, the alkalinegas can be supplied into the bell jar 12 from the gas supplying source71. On the other hand, by closing the valve 75 and opening the valves 76and 78, the acid gas can be supplied into the bell jar 12 from the gassupplying source 72.

Note that, by dissolving the alkaline gas and the acid gas in theslurry, a pH value of the slurry can be adjusted.

Other acid gasses, e.g., hydrochloric acid gas, nitric acid gas, may beused in the polishing apparatus.

A pH detecting unit 80 detects the pH value of the slurry in the belljar 12 or passing through the pipe 44, etc.

Another example of the driving unit is shown in FIG. 5.

A motor 64 a including a stator 62 a and a rotor 63 a is provided in thebell jar 12, and the polishing plate 23 is fixed on the rotor 63 a. Amotor driver 65 a is provided outside of the bell jar 12, and electricpower is supplied to stator coils via wires 66. Note that, the motor 64a is a known electric motor.

In this driving unit, only the wires 66 should be sealed, therefore thesealing mechanism can be simplified.

Further, another example of the driving unit is shown in FIG. 6.

In this example, the polishing plate 23 is rotated by magnetic couplermeans. Namely, a first magnet rotor 67, in which North magnetic polesand South magnetic poles are alternately formed on an outercircumferential face, is rotated by a motor 68. By rotating the firstmagnet rotor 67, a second magnet rotor 69 is rotated. The polishingplate 23 is fixed on the second magnet rotor 69.

With this structure, the polishing plate 23 can be rotated withoutcontacting any members located outside, therefore an inner space of thebell jar 12 can be maintained clean.

In the present embodiment, the polishing plate 23 is rotated about itsown axis. In another embodiment, the polishing plate 23 may be moved ina plane parallel to a polishing face (the polishing pad) of thepolishing plate 23. This embodiment is shown in FIG. 7.

In FIG. 7, a plurality of crank shafts 70 are attached to the polishingplate 23, and the crank shafts 70 are synchronously rotated by a drivingunit (not shown), which is provided outside of the bell jar 12. Withthis structure, the polishing plate 23 can be moved along a circularorbit with fixed heading. Namely, all points in the polishing plate 23equally rotate in a direction “B”.

In the above described embodiment, the work piece is merely pressed ontothe polishing plate 23 by the pressing plate 36. The work piece may beadhered on a bottom face of the pressing plate 36. In this case, thepolished work piece is peeled from the pressing plate 36 when thepolishing is completed.

The pressing member 36 may have sucking means for holding the work pieceby producing negative pressure. In this case, the sucking means may suckand hold the work piece directly or with an elastic bucking member.

In the above described embodiment, the weights 37 are employed as thepress unit. A cylinder unit (not shown) provided on the arm 40 may beemployed to apply pressure to the work piece.

Further, a pressure head-type pressing plate may be employed. An exampleof the pressure head-type pressing plate 36 is shown in FIG. 8.

A holding member 73 a is suspended in a head proper 72 a by an elasticring member 74 a, e.g., diaphragm. With this structure, a pressurechamber 75 a is formed. The pressurized fluid is introduced into thepressure chamber 75 a, so that the work piece held on a bottom face ofthe holding member 73 a is pressed onto the polishing plate 23.Preferably, the pressing plate 36 is rotated about a rotary shaft 76 aby a motor (not shown). A driving mechanism including the motor may beprovided on the arm 40.

Further, the pressing plate 36 may be vertically moved by a cylinderunit (not shown) so as to move to and away from the polishing face (thepolishing pad) of the polishing plate 23. In this case, the rotary shaft76 a may be rotatably held by a holding arm (not shown), and the holdingarm may be vertically moved by a cylinder unit (not shown) provided onthe arm 40.

The driving mechanism allows the rotary shaft 76 a to vertically move ina prescribed range and transmits torque of the motor.

The pressurized fluid is introduced into the pressure chamber 75 a via afluid path 77 a formed in the rotary shaft 76 a. The fluid is introducedinto the fluid path 77 a via a rotary joint (not shown).

A restraining ring 78 a prevents the holding member 73 a from coming outfrom the head proper 72 a and guides the vertical movement of theholding member 73 a.

An O-ring 79 a is provided between an inner circumferential face of thehead proper 72 a and an outer circumferential face of the holding member73 a. The O-ring 79 a absorbs horizontal movement of the holding member73 a and prohibits the slurry to enter the head proper 72 a.

Experiments were executed in the polishing apparatus 10 under thefollowing conditions. Note that, the inner air pressure of the bell jar12 was varied; and the copper layer, the SiO₂ layer and the Si substrateof the work piece were polished.

The conditions were,

-   -   Polishing pad: IC 1000/SUBA400 (trade name), diameter 200 mm;    -   Slurry: silica slurry “SS-25” for SiO₂    -    colloidal silica “Compol-80” for Si    -    alumina slurry for Copper (no oxidizing agent were added);    -   Pressing force of the pressing plate 36: 100-500 g/cm²;    -   Rotational speed of the polishing plate 23: 15-90 rpm; and    -   Polishing time: 2-4 min.

The work piece were polished with the fixed pressing force, the fixedrotational speed and the fixed polishing time under above conditions.The results are shown in FIG. 9.

In FIG. 9, the inner pressure of zero is the atmospheric pressure.Namely, the horizontal axis or the inner pressure of the bell jar 12indicates the pressure added to and reduced from the atmosphericpressure.

As clearly shown in FIG. 9, polishing rate under the atmosphericpressure was minimum; the polishing rate was increased in nearlyproportion to increasing and reducing the inner pressure.

Especially, in the case of polishing the SiO₂ layer and the Sisubstrate, the polishing rate of 200 kPa was about twice as great asthat of the atmospheric pressure; and the polishing rate of 500 kPa wasabout 2.5 times as great as that of the atmospheric pressure.

In case of polishing the copper layer, the minimum polishing rateappeared on the negative pressure side (about −50 kPa). Namely, theminimum polishing rate was slightly shifted toward the negative pressureside, but the polishing rate was increased on the both sides of theminimum as well as the SiO₂ layer and the Si substrate.

The inventor thinks that the reasons of increasing the polishing rateunder the positive pressure are: the fluid pressure is applied to thepressing plate 36; and the slurry is permeated into the polishing pad bythe fluid pressure.

The reason of increasing the polishing rate under the negative pressureis not clearly found. The inventor thinks that frictional heat betweenthe work piece and the polishing pad is hardly radiated due to pressurereduction in the bell jar 12 so that temperature rises and reaction rateis increased. By increasing the reaction rate, the polishing rate isincreased under the negative pressure.

FIG. 10 is a graph showing a relationship between oxygen gas pressureand the polishing rate. Oxygen was used as the fluid instead of the air.

Tendency of the case of employing oxygen is nearly equal to that of thecase employing the air. Especially, in the case of polishing the copperlayer, the polishing rate was much increased under high pressure.

According to the results, the polishing rate can be controlled byadjusting the inner pressure of the bell jar 12 without changing otherconditions.

For example, when the polishing is started and the work piece is roughlypolished, the inner pressure of the bell jar 12 is increased or reducedso as to polish the work piece with high polishing rate; when the workpiece is finished and the work piece, the inner pressure of the bell jar12 is returned to zero or the atmospheric pressure so as to polish thework piece with low polishing rate.

Of course, the polishing rate may be controlled by combining otherfactors, e.g., the rotational speed of the polishing plate 23.

In case of using a plurality of kinds of slurry or polishing pads, aplurality of polishing stations are provided in one polishing apparatus,so that the polishing apparatus must be large. However, the innerpressure of the bell jar 12 and the rotational speed of the polishingplate 23 can be changed at one polishing station, so number of thepolishing stations can be reduced, the polishing conditions can beeasily determined, a size of the polishing apparatus can be smaller andmanufacturing cost of the apparatus can be reduced.

The slurry accommodated in the bell jar 12 is pressurized andcirculated, so load of the circulation pump 43 is not so great.

If the slurry storing section is provided outside of the bell jar 12,the slurry is introduced into the bell jar 12 whose inner pressure hasbeen increased, so that a high power circulation pump is required.

The slurry may stay in the bell jar 12. In this case, the polishingplate 23 is inclined with respect to the horizontal plane, by adjustingthe adjustable bolts 33, so as to dip a lower part of the surface of thepolishing plate 23 in the slurry. With this structure, the slurry can bealways permeated into the polishing pad for polishing the work piece.

Next, adjusting a pH value of the slurry will be explained.

Note that, the adjustment of the pH value and the adjustment of theinner pressure of the bell jar 12 may be executed separately orsimultaneously.

FIG. 11 shows polishing efficiency with slurry “CU-5001 (trade name ofCabot Co., USA)”.

The slurry is usually used for polishing copper, its pH value is about7, and a proper amount of hydrogen peroxide is usually added to theslurry.

Experiments were performed with (1) the slurry with hydrogen peroxide,(2) the slurry with no hydrogen peroxide and (3) the slurry with nohydrogen peroxide but an alkaline liquid, e.g., aqua ammonia, was addedto increase the pH value to about 10. The bell jar 12 was pressurized byan oxygen gas, and copper layers were polished with the slurry (1)-(3).The results are shown in FIG. 11.

In FIG. 11, the inner pressure of 0 kpa is the atmospheric pressure.Namely, the horizontal axis or the inner pressure of the bell jar 12indicates the pressure added to and reduced from the atmosphericpressure. On the other hand, the vertical axis indicates relativepolishing rate.

As clearly shown in FIG. 11, the polishing rate of the slurry withhydrogen peroxide was 2-3 times greater than that with no hydrogenperoxide; the polishing rate of the slurry with hydrogen peroxide wasnot increased by increasing and reducing the inner oxygen gas pressureof the bell jar 12.

In case of the slurry to which the alkaline liquid was added, dependenceon the inner pressure of the bell jar 12 was very high, and thepolishing rate of the slurry to which the alkaline liquid was added was3-4 times greater than that with hydrogen peroxide.

According to the results, the polishing rate of slurry highly depends onthe pH value and the inner pressure of the bell jar 12. Therefore, thepolishing rate can be controlled by adjusting the pH value of the slurryand the inner pressure of the bell jar 12.

FIG. 12 shows a relationship between polishing rate of ordinary slurryfor polishing SiO₂ film, glass, quartz, etc. and pH value of the slurry.Note that, the inner space of the bell jar 12 was not pressurized duringthe experiments. A graph “A” was the slurry including ceria (cerium)grains; a graph “B” was the slurry including silica (SiO₂) grains.Maximum polishing rate of the ceria slurry was observed when the pHvalue was about 7, and the polishing rate thereof was reduced on thealkaline side and the acid side. On the other hand, maximum polishingrate of the silica slurry was observed when the pH value was 9-10.

FIG. 13 shows a relationship between polishing rate of slurry forpolishing copper, tantalum, tantalum nitride, etc. and pH value of theslurry. Note that, the inner space of the bell jar 12 was notpressurized during the experiments. A graph “C” was the slurry forpolishing copper, and maximum polishing rate was observed when the pHvalue was about 3-4 (the acid side). Note that, the slurry was differentfrom the Cabot slurry of FIG. 11. On the other hand, a graph “D” was theslurry for polishing tantalum and tantalum nitride, and maximumpolishing rate was observed when the pH value was about 3-4 (the acidside). Tantalum and tantalum nitride are very hard substances, so thepolishing rate of the slurry for polishing tantalum and tantalum nitridewas much lower than that of the slurry for polishing copper.

The slurry of FIGS. 12 and 13 are usually selectively used according towork pieces to be polished.

As described above, a work piece or work pieces are polished in theclosed bell jar 12.

Since the bell jar 12 is air-tightly closed, the pH value of the slurryin the bell jar 12 can be changed in real time by supplying the alkalinegas or the acid gas from the gas supplying source 71 or 72. Note that,the gas in the bell jar 12 can be discharged by the gas dischargingsection 48.

The pH value of the slurry can be changed by the alkaline gas and theacid gas because the bell jar 12 is air-tightly closed. Namely, theslurry in the bell jar 12 is not influenced by external atmosphericconditions.

Since the pH value of the slurry can be changed in real time, thepolishing rate can be changed without changing slurry. Namely, variouskinds of polishing can be executed with the same slurry. The polishingrate may be controlled by changing the pH value without changingpressure of the pressurizing gas in the bell jar 12. Further, assuggested in FIG. 11, the polishing rate may be controlled by changingthe pH value and the pressure of the pressurizing gas in the bell jar12.

An example of the control of the polishing rate will be explained withreference to FIGS. 14-17. FIGS. 14-17 show a process of implantingcopper cables coated with a SiO₂ film 60 in a substrate.

A barrier metal layer 61 prevents copper 62 from diffusing in the SiO₂film 60. The barrier metal layer 61 is formed by spattering tantalumnitride (TaN) or tantalum (Ta). The copper layer 62 is formed by, forexample, electrolytic copper plating.

Firstly, as shown in FIG. 15, the copper layer 62 is polished close tothe barrier metal layer 61 with slurry, e.g., the slurry “C” of FIG. 13.When the copper layer 62 is polished, the inner air pressure of the belljar 12 is highly increased and the pH value is adjusted about 3.Therefore, the copper layer 62 can be polished with high polishing rate.

Next, as shown in FIG. 16, the copper layer 62 is further polished, withmoderate polishing rate, until the barrier metal layer 61 is exposed. Inthis polishing process, the inner pressure of the bell jar 12 isslightly reduced to moderate pressure, then the ammonia gas isintroduced into the bell jar 12 to make the pH value of the slurry about6. If this polishing process is executed with high polishing rate, thecopper layer 62, which is softer than the barrier metal layer 61, isover-polished so that flatness of the polished surface is lowered.

Finally, the inner pressure of the bell jar 12 is returned to theatmospheric pressure, and the pH value of the slurry is increased to 7or 8 by supplying the ammonia gas into the bell jar 12. Top parts of thebarrier metal layer 61 are removed by polishing with lower polishingrate. With this process, the implanted cables can be formed with highflatness (see FIG. 17).

FIGS. 18-21 show an example of polishing a SiO₂ film 64 formed on coppercables 63. Note that, a symbol 65 stands for stop layers made of, forexample, tantalum nitride.

For example, the slurry “A” of FIG. 12 is used for polishing, the pHvalue of the slurry is about 7, the inner pressure of the bell jar 12 isincreased by supplying air, and the SiO₂ film 64 is efficiently polishedclose to the stop layers 65 (see FIG. 19) with high polishing rate.

Next, as shown in FIG. 20, the SiO₂ film 64 is further polished, withmoderate polishing rate, until the stop layers 65 are exposed. In thispolishing process, the inner pressure of the bell jar 12 is slightlyreduced to moderate pressure, then the carbonic acid gas is introducedinto the bell jar 12 to make the pH value of the slurry about 5.

Finally, the pH value of the slurry is adjusted about 3 by furthersupplying the carbonic acid gas into the bell jar 12, and the innerpressure of the bell jar 12 is returned to the atmospheric pressure. Thestop layers 65 are removed by polishing with lower polishing rate. Withthis process, the implanted cables can be formed with high flatness (seeFIG. 21).

As described above, the work piece can be highly efficiently polished inthe same bell jar 12 without exchanging the slurry.

Another embodiment of the polishing apparatus 10 is shown in FIG. 22.The structural elements shown in FIG. 4 are assigned the same symbolsand explanation will be omitted.

In this embodiment, pure water is used as slurry, and the alkaline gasand the acid gas are supplied into the pure water so as to adjust the pHvalue of the slurry (water).

The pure water is stored in a pure water source 82, e.g., tank. The purewater is supplied into the body proper 16 of the bell jar 12 from thepure water source 82 by a pump 83 via a pipe 84. A valve 85 is providedto the pipe 84.

A method of preparing the slurry in the body proper 16 will beexplained.

Firstly, a suitable amount of pure water is supplied into the bodyproper 16 from the pure water source 82. Note that, in case of preparingslurry including polishing grains, a suitable amount of polishing grainsare also supplied into the body proper 16 from a grain supplying section(not shown). For example, in case of polishing copper film, no polishinggrains are required.

In the polishing apparatus 10 of the present embodiment, the alkalineslurry or the acid slurry is selected according to work pieces to bepolished. The pH value of the slurry is easily adjusted by supplying thealkaline gas or the acid gas into the body proper 16 from the gassupplying source 71 or 72. Namely, the pH value is adjusted by solelydissolving the alkaline gas or the acid gas in the pure water. Since thebell jar 12 can be air-tightly closed, the pH value can be easilyadjusted. Amount of supplying the alkaline gas or the acid gas can beadjusted by detecting the pH value of the slurry with the pH detectingunit 80.

Further, polishing grains may be supplied into the slurry if required.

In the present embodiment too, the pH value of the slurry in the belljar 12 can be adjusted in real time. Therefore, the polishing processesshown in FIGS. 14-17 and FIGS. 18-21 can be executed.

Firstly, the process of polishing implanting copper cables coated with aSiO₂ film 60 will be explained with reference to FIGS. 14-17.

The barrier metal layer 61 prevents the copper layer 62 from diffusingin the SiO₂ film 60. The barrier metal layer 61 is formed by spatteringtantalum nitride (TaN) or tantalum (Ta). The copper layer 62 is formedby, for example, electrolytic copper plating.

To polish the copper layer 62, the pure water and the acid gas aresupplied into the body proper 16 so as to make the slurry whose pH valueis about 3. As described above, polishing grains may be supplied ifrequired.

As shown in FIG. 15, the copper layer 62 is polished close to thebarrier metal layer 61 with this slurry. When the copper layer 62 ispolished, the inner air pressure of the bell jar 12 is highly increasedand the pH value is adjusted about 3. Therefore, the copper layer 62 canbe polished with high polishing rate.

Next, as shown in FIG. 16, the copper layer 62 is further polished, withmoderate polishing rate, until the barrier metal layer 61 is exposed. Inthis polishing process, the inner pressure of the bell jar 12 isslightly reduced to moderate pressure, then the ammonia gas isintroduced into the bell jar 12 to make the pH value of the slurry about6. If this polishing process is executed with high polishing rate, thecopper layer 62, which is softer than the barrier metal layer 61, isover-polished so that flatness of the polished surface is lowered.

Finally, the inner pressure of the bell jar 12 is returned to, forexample, the atmospheric pressure, and the pH value of the slurry isincreased to 7 or 8 by supplying the ammonia gas into the bell jar 12.Top parts of the barrier metal layer 61 are removed by polishing withlower polishing rate. With this process, the implanted cables can beformed with high flatness (see FIG. 17).

In this process, the acid slurry is firstly prepared, then the ammoniagas is supplied to the acid slurry. Therefore, salt is formed in theslurry by neutralization, but the salt does not badly influence thepolishing.

As described above, the implanted copper cables can be polished.

To newly execute another polishing process, the slurry is completelydrained from the bell jar 12, the polishing pad is cleaned with purewater, then new slurry is prepared. In the present embodiment, theslurry is formed by merely dissolving the alkaline component or the acidcomponent in the pure water. Polishing grains may be included ifrequired. Therefore, the polishing pad can be easily cleaned, and thenew slurry can be prepared in a very short time.

Therefore, a cycle time of the polishing process can be shortened, andthe polishing efficiency can be improved.

Successively, another example of polishing the SiO₂ film 64 formed oncopper cables 63 will be explained with reference to FIGS. 18-21. Notethat, the symbol 65 stands for stop layers made of, for example,tantalum nitride.

As described above, a suitable pH value of the slurry for polishing theSiO₂ film 64 is about 7. Slurry is prepared by supplying the pure waterinto the body proper 16. The SiO₂ film 64 can be well polished by theslurry including polishing grains, so polishing grains may be suppliedinto the slurry from the grain supplying section.

To polish the SiO₂ film 64 close to the stop layers 65 (see FIG. 19)with this slurry, the inner pressure of the bell jar 12 is increased bysupplying air, and the SiO₂ film 64 is efficiently polished with highpolishing rate.

Next, as shown in FIG. 20, the SiO₂ film 64 is further polished, withmoderate polishing rate, until the stop layers 65 are exposed. In thispolishing process, the inner pressure of the bell jar 12 is slightlyreduced to moderate pressure, and the carbonic acid gas is introducedinto the bell jar 12 to make the pH value of the slurry about 5.

Finally, the pH value of the slurry is adjusted about 3 by furthersupplying the carbonic acid gas into the bell jar 12, and the innerpressure of the bell jar 12 is returned to, for example, the atmosphericpressure. The stop layers 65 are removed by polishing with lowerpolishing rate. With this process, the implanted cables can be formedwith high flatness (see FIG. 21).

As described above, the work piece can be highly efficiently polished inthe same bell jar 12 without exchanging the slurry.

When another polishing process is executed, the slurry may be completelyexchanged. In this case too, the slurry can be easily prepared.

In the present invention, a neutral gas, e.g., ozone, oxygen,hydrogencarbonate gas, may be supplied into the bell jar 12, as a gasfor preparing the slurry, instead of the alkaline gas and the acid gas.In this case, the neutral gas is not supplied from the gas supplyingsources 71 and 72, but it may be supplied from the pressurizing unit 47,as the gas for preparing the slurry and for increasing the innerpressure of the bell jar 12.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by he foregoing descriptionand all changes which come within the meaning and range of equivalencyof the claims are therefore intended to be embraced therein.

1. A polishing apparatus, comprising: a pressure vessel having a lidwhich opens or closes said pressure vessel; a polishing plate beingprovided in said pressure vessel; a pressing plate being provided onsaid polishing plate, said pressing plate pressing a work piece, whichhas been set between said polishing plate and said pressing plate, ontosaid polishing plate; a driving unit relatively moving said polishingplate with respect to said pressing plate so as to polish the workpiece; a gas supplying source being connected to said pressure vessel,said gas supplying source supplying an alkaline gas or an acid gas intosaid pressure vessel; a gas discharging section discharging the suppliedgas from said pressure vessel; and a slurry supplying unit supplyingslurry onto said polishing plate, wherein a pH value of the slurry isadjusted by dissolving the alkaline gas or the acid gas in the slurry.2. The polishing apparatus according to claim 1, further comprising apressure source supplying a pressurizing gas, which is different fromthe alkaline gas and the acid gas, into and sucking the same from saidpressure vessel so as to increase or reduce inner pressure of saidpressure vessel.
 3. The polishing apparatus according to claim 1,further comprising a pH detecting unit for detecting the pH value of theslurry.
 4. The polishing apparatus according to claim 2, furthercomprising a pH detecting unit for detecting the pH value of the slurry.5. A polishing apparatus, comprising: a pressure vessel having a lidwhich opens or closes said pressure vessel; a polishing plate beingprovided in said pressure vessel; a pressing plate being provided onsaid polishing plate, said pressing plate pressing a work piece, whichhas been set between said polishing plate and said pressing plate, ontosaid polishing plate; a driving unit relatively moving said polishingplate with respect to said pressing plate so as to polish the workpiece; a gas supplying source being connected to said pressure vessel,said gas supplying source supplying an alkaline gas or an acid gas intosaid pressure vessel; a gas discharging section discharging the suppliedgas from said pressure vessel; and a pure water supplying unit supplyingpure water onto said polishing plate, wherein a pH value of the purewater is adjusted by dissolving the alkaline gas or the acid gas in thepure water so as to use the pure water as slurry.
 6. The polishingapparatus according to claim 5, further comprising a pressure sourcesupplying a pressurizing gas, which is different from the alkaline gasand the acid gas, into and sucking the same from said pressure vessel soas to increase or reduce inner pressure of said pressure vessel.
 7. Thepolishing apparatus according to claim 5, further comprising a pHdetecting unit for detecting the pH value of the pure water.
 8. Thepolishing apparatus according to claim 6, further comprising a pHdetecting unit for detecting the pH value of the pure water.
 9. A methodof polishing a work piece in a polishing apparatus comprising: apressure vessel having a lid which opens or closes said pressure vessel;a polishing plate being provided in said pressure vessel; a pressingplate being provided on said polishing plate, said pressing platepressing a work piece, which has been set between said polishing plateand said pressing plate, onto said polishing plate; a driving unitrelatively moving said polishing plate with respect to said pressingplate so as to polish the work piece; a gas supplying source beingconnected to said pressure vessel, said gas supplying source supplyingan alkaline gas or an acid gas into said pressure vessel; a gasdischarging section discharging the supplied gas from said pressurevessel; and a slurry supplying unit supplying slurry onto said polishingplate, said method comprising the step of: supplying the alkaline gas orthe acid gas into said pressure vessel from said gas supplying source soas to adjust the pH value of the slurry.
 10. The method according toclaim 9, further comprising the step of supplying a pressurizing gas,which is different from the alkaline gas and the acid gas, into saidpressure vessel or sucking the pressurizing gas therefrom, by a pressuresource, so as to increase or reduce inner pressure of said pressurevessel.
 11. The method according to claim 9, further comprising the stepof detecting the pH value of the slurry by a pH detecting unit.
 12. Themethod according to claim 10, further comprising the step of detectingthe pH value of the slurry by a pH detecting unit.
 13. A method ofpolishing a work piece in a polishing apparatus comprising: a pressurevessel having a lid which opens or closes said pressure vessel; apolishing plate being provided in said pressure vessel; a pressing platebeing provided on said polishing plate, said pressing plate pressing awork piece, which has been set between said polishing plate and saidpressing plate, onto said polishing plate; a driving unit relativelymoving said polishing plate with respect to said pressing plate so as topolish the work piece; a gas supplying source being connected to saidpressure vessel, said gas supplying source supplying an alkaline gas oran acid gas into said pressure vessel; a gas discharging sectiondischarging the supplied gas from said pressure vessel; and a pure watersupplying unit supplying pure water onto said polishing plate, saidmethod comprising the step of: supplying the alkaline gas or the acidgas into said pressure vessel from said gas supplying source so as toadjust the pH value of the pure water and use the pure water as slurry.14. The method according to claim 13, further comprising the step ofsupplying a pressurizing gas, which is different from the alkaline gasand the acid gas, into said pressure vessel or sucking the pressurizinggas therefrom, by a pressure source, so as to increase or reduce innerpressure of said pressure vessel.
 15. The method according to claim 13,further comprising the step of detecting the pH value of the pure waterby a pH detecting unit.
 16. The method according to claim 14, furthercomprising the step of detecting the pH value of the pure water by a pHdetecting unit.